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Resource summary

1 A box and whisker plot is used to display information about the
range, the median and the quartiles. It is usually drawn alongside
a number line, as shown

Annotations:

A box and whisker plot is used to display information about the range, the median and the quartiles. It is usually drawn alongside a number line,

1.1

2 Example The oldest person in Mathsminster is 90. The youngest person is 15. The median age of the
residents is 44, the lower quartile is 25, and the upper quartile is 67. Represent this information with
a box-and-whisker plot. Solution A box plot diagram

2.1 Upper Quartile

2.1.1 upper quartile or the 75th percentile (splits off the highest 25% of data from the lowest 75%)

2.2

3 lower
quartile

3.1 The 25th percentile

4 inter quartile-The interquartile range is
the difference between the upper quartile
and lower quartile.

5

6 WORKING OUT UPPER,LOWER AND INTERQUARTILE RANGE

6.1 lOWER

6.2 UPPER

6.2.1

7 The "interquartile range", abbreviated "IQR", is just the width of the box in the box-and-whisker plot. That is, IQR = Q3 – Q1. The
IQR can be used as a measure of how spread-out the values are. Statistics assumes that your values are clustered around some
central value. The IQR tells how spread out the "middle" values are; it can also be used to tell when some of the other values are
"too far" from the central value. These "too far away" points are called "outliers", because they "lie outside" the range in which we
expect them.